Fluidized bed of solid particles, and method of using it

ABSTRACT

Fluidized bed comprises discrete particles of alumina trihydrate, and a gas such as air or sulfur hexafluoride is directed through particles to fluidize them. Fluidized bed may be used as a cooling medium for electrical apparatus, such as transformers, and as a medium to assist in extinguishing the arc between switch contacts.

- United States Patent Moller [451 Jan. 25, 1972 [54] FLUIDIZED BED OFSOLID I PARTICLES, AND METHOD OF USING IT [72] Inventor: Werner Moller,Dubendorf, Switzerland [73] Assignee: Oerlikon Engineering Company [22]Filed: May 3, 1968 [21] Appl. No.: 726,598

30 Foreign Application Priority Data May 12, 1967 Switzerland ..6816/67[52] US. Cl. ..200/148 G, 200/144 C, 200/149 A, 252/463, 23/142 [51]Int. Cl. ..HOlh 33/22 [58] Field of Search 174/174 AT; 336/57;ZOO/144.3, ZOO/149.1, 151, 149 A; 252/463; 23/142 Primary Examiner-Robert S. Macon Attorney-Breitenfeld & Levine [57] ABSTRACT Fluidizedbed comprises discrete particles of alumina trihydrate, and a gas suchas air or sulfur hexafluoride is directed through particles to fluidizethem. Fluidized bed may be used as a cooling medium for electricalapparatus, such as transformers, and as a medium to assist inextinguishing the arc between switch contacts.

4 Claims, No Drawings FLUIDIZED BED F SOLID PARTICLES, AND METHOD OFUSING IT The present invention relates to a fluidized bed, in which apulverized solid is moved by means of a gas, and also to the use of sucha bed.

Fluidized beds incorporating solid discrete particles are known in theprior art in which quartz sand, corundum, and plastics are used as thesolid particles, and air, carbon dioxide, and hydrogen as the fluidizinggases. Corundum and quartz sand, are disadvantageous, because, interalia, they produce an extremely large amount of abrasion; plastics onthe other hand exhibit low resistance to heat. In addition, frequently auniform bed of solids cannot be readily obtained and the required gaspressures are relatively high.

The deficiencies of the prior art can be avoided, in accordance with theinvention, by employing alumina trihydrate (aluminum oxide trihydrate)as the solid particles. In accordance with other features of theinvention, the fluidized bed may be used to insulate and cool electricalinstruments and apparatus.

Either air or sulfur hexafluoridemay be used as the fluidizing gas.

The size of the alumina trihydrate particles should be between 5 and 100microns, and preferably [0 microns. The gas velocity should be between0.3 and 0.7 meter per second, and is preferably 0.5 meter per second.

The advantages of the invention reside not only in reduced cost ascompared to prior art beds, but also, inter alia, in that abrasion issubstantially avoided, and there is no danger of the formation ofcrusts. Furthermore, the formation of a fluidized bed is possible evenwith a low-pressure fluidizing gas. The bed also has excellentelectrical and thermal properties.

The fluidized bed of solid particles can advantageously be used intransformers. In this case, it is merely necessary to circulate the gasthrough a cooling circuit while the level of the bed of solids remainsapproximately the same. Alternatively,

the entire bed could be circulated, and if necessary cooled from time totime. Investigations have shown that when the techniques described aboveare used, no changes due to aging occur in the customary insulation of atransformer. Furthermore, heat transfer takes place just as rapidly aswhen transformer oil is used as the coolant, and much more rapidly thanwhen air alone is used. Improved heat transfer with respect to air aloneis believed to be due to the fact that the thermal conductivity of theparticles of the fluidized bed exceeds that of air.

When the fluidized bed of solid particles is used as an assist inextinguishing the arc of electrical switches, the corrosivedecomposition products of sulfur hexafluoride, particularly sulfurdifluoride and sulfur tetrafluoride, which are produced in the arc areconverted into harmless products, particularly aluminum fluoridecompounds.

What is claimed is:

l. A fluidizable bed comprising a bed of solid discrete particles,substantially all of said particles being alumina trihydrate, and meansfor directing sulfur hexafluoride gas through the bed to fluidize saidparticles.

2. A method of cooling electrical apparatus having a path foraccommodating a cooling fluid, comprising the steps of providing a bedformed substantially entirely of discrete alumina trihydrate particles,fluidizing the particles by means of a gas, and directing the gas andfluidized particles along the path.

3. A method as defined in claim 2 wherein the apparatus is atransformer.

4. A method as defined in claim 2 wherein the apparatus is a switch, thepath includes the switch contacts, and said gas and fluidized particlesare directed along the path while the switch is opened so that theyassist in extinguishing the are which forms between the contacts.

2. A method of cooling electrIcal apparatus having a path foraccommodating a cooling fluid, comprising the steps of providing a bedformed substantially entirely of discrete alumina trihydrate particles,fluidizing the particles by means of a gas, and directing the gas andfluidized particles along the path.
 3. A method as defined in claim 2wherein the apparatus is a transformer.
 4. A method as defined in claim2 wherein the apparatus is a switch, the path includes the switchcontacts, and said gas and fluidized particles are directed along thepath while the switch is opened so that they assist in extinguishing thearc which forms between the contacts.